1. Field of the Invention
This invention pertains generally to a twist lock pin for a modified shackle, and more particularly to a spring loaded shackle system with a twist lock pin that securely locks into a modified shackle with a combination push and twist.
2. Description of Related Art
A cross bolt shackle is commonly used as a lifting tool in the marine and construction industries for lifting, slinging, securing loads and other purposes. A typical shackle has a U shape forming two legs and has aligned eyes or apertures at the end of each leg. A bolt or pin, usually with a bolt type head at one end, is inserted through the eyes and through an aperture such as a chain link, cable loop, lifting lug, rod end, or the like, positioned between the eyes. Many shackles use one threaded eye to accommodate a mating threaded cross pin. Many others use a hitch pin or cotter pin through the end of the shaft of the cross pin outside the shackle eye.
It is very important that a cross pin does not become unsecured during use from vibration, shaking or jarring. Thus, a variety of securing devices have been developed for shackle cross pins. For example, there are shackles with threaded lock nuts, cam locks or jam blocks to prevent a threaded cross pin from rotating after insertion. There are cross pins that use slots in the shackle eyes and mating protrusions or lugs on a cross pin that must be aligned before insertion and rotated to a secure position. Other devices put slots or keyways in the cross pin and mating protrusions on the shackle eye. Hitch pins with a central actuator and spring loaded ball locks or protrusions on the end are also used for securing shackle cross pins.
Each of these previous solutions has shortcomings, however, especially when using the aforementioned shackle and cross pin combinations in heavy lifting. For example, cross pins with central actuators also have a central bore that weakens the pin making them unsuitable for heavy loads. Cross pins with threads, slots and protrusions are subject to jamming or damage when the shackle and pin are exposed to mud, sand, debris, etc. Shackle and cross pins with mating slots and protrusions and threaded cross pins are particularly susceptible to dents, dings and strikes from hard objects that damage or deforms the threads, slot or protrusion. Further, the slots and protrusions must be aligned before advancing the pin and supporting the load. Another problem with some existing shackles and cross pins is they require two hands to secure and unsecure. This is not suitable for situations where the worker must support a chain or cable in the shackle with one hand and secure the shackle pin with the other. A visual or tactile indication of engagement is inadequate or non-existent on some shackle and pin arrangements. Some shackle systems, including systems with cotter pins or hitch pins in the cross pin, require visual and/or tactile access to both sides of the shackle to secure the pin. Still others have pinch points on the surfaces of the shackle and pin that menace skin, fingers and hands. Many of the complex solutions require several time consuming motions to secure and unsecure, or thread and unthread the cross pin. Still others are not suitable for manipulation and engagement while wearing heavy construction or winter gloves.
What is needed is a shackle and cross pin system that is suitable for heavy loads in adverse construction and marine conditions and can be quickly secured and unsecured with one hand while wearing heavy gloves. A shackle and cross pin system is also needed that minimizes pinch points, has a tactile indication of engagement, and does not require blind side access to the shackle. A system that is inexpensive to manufacture or can be installed or retrofitted on existing shackles is desirable. A shackle and pin system where the pin can partially support a load before engagement is also desirable.